1. Field of the Invention
The present invention is generally related to an organic light-emitting diode (OLED), and more particularly to an OLED containing an Ir (iridium) complex as a phosphorescent emitter where pyridyl triazole or pyridyl imidazole is used as an auxiliary mono-anionic bichelate ligand for the Ir complex.
2. Description of the Prior Art
At present, phosphorescent metal complex has been utilized as a phosphorescent dopant for organic light-emitting diodes (OLEDs). Among these metal complexes used in the emitter of OLEDs, Ir complexes have been comprehensively studied because of its strong spin-orbital coupling property in the electron configuration. Since the spin-orbital coupling causes mixing between the singlet state and the triplet state, the lifetime of the triplet state is thus reduced to thereby increase phosphorescence efficiency. Generally, these Ir complexes have regular octahedron structures containing positive trivalent oxidation states. The light emitting mechanism comes from emission of the triplet metal-to-ligand charge-transfer transition state (3MLCT state) or the ligand triplet state (3π-π).
US published patent application no. US2002/0034656A1 discloses metal complexes as phosphorescent emitters, comprising octahedron complexes L2MX (M=Ir, Pt) using vinylpyridine (L) as ligands where the Ir complexes comprise of various N—C heterocyclic ligands and Ir.
On the other hand, the research reports published by the department of chemistry, National Tsing Hua University in various journals (referring to References 1-3) disclose some diazoheterocyclic compounds used as the third ligand for Ir complexes.
Taiwan patent application no. 93137789 applied by the assignee of the present invention discloses an Ir complex as phosphorescent emitters in OLEDs, using benzoimidazole as mono-anionic bichelate ligands.